A recent booklet has a page with high bending rigidity as part of tendency to heighten the added value. For example, there is a booklet having an ID page given a security protective layer to prevent forgery countermeasures of personal information, or a plastic sheet page having a buried IC chip for high-density recording. Another booklet has a radio IC chip readable and writable without contact. A front or back cover of such a booklet is given a radio shielding function to protect recorded information from unauthorized reading or writing. Such a booklet accepts reading or writing only when a front cover is opened.
An ordinary booklet page turning apparatus causes buckling distortion in a booklet, assuming the low bending rigidity of a booklet, turns up a page with a page turning roller, and flips up the page on the page turning roller.
However, when an ordinary page turning apparatus attempts to turn a rigid page of a booklet, the difference between the frictional force between the page turning roller and the uppermost page and the friction force between the uppermost page and the page under the uppermost page does not meet the condition to cause buckling distortion in the rigid page.
If the page turning roller is changed to the one with higher frictional coefficient, it can cause buckling distortion in a booklet. However, in this case, a rigid page may suffer plastic deformation exceeding over its plastic deformation range, or a buried IC chip may suffer stress destruction. Therefore, in the prior art, a page turning roller contacts the end of a booklet, and is raised while rotating, thereby a rigid page is turned without buckling distortion (e.g., Japanese Patent Application Publication No. 2005-144756).
However, in this method, the end of a rigid page must be accurately detected and made to contact the page turning roller, otherwise the page cannot be turned up.
Besides, pages of a booklet are fixed at the bound edge of a booklet like a cantilever structure, and tend to bend and become uneven at the ends after being repeatedly turned up and down, increasing the unstable elements of the page turning operation.
In a booklet having a rigid page mixed with ordinary body pages, after the rigid page and body pages are repeatedly turned up and down, the bending and unevenness of the ends of the pages are accelerated, and the unstable elements of the page turning operation are increased.
As described above, a booklet having two or more rigid pages is difficult to stably turn the pages by using page turning rollers.
As a method of separating a sheet one by one from a stack and conveying each sheet, a negative suction method using a vacuum pad is well known.
This method does not depend on the rigidity of a medium, and is advantageous to a booklet including two or more rigid pages.
A vacuum pad is available in various types according to the properties of a medium. One type of vacuum pad has an axle of rotation for oscillation. Another type of vacuum pad is deformable (made of rubber material or shaped like bellows).
However, if such a negative suction method is simply applied to a booklet page turning apparatus, the pages of a booklet cannot be turned unless each page of a booklet is raised by turning up over 90 degree with respect to the bound edge of a booklet, and a travel of a vacuum pad is increased. This makes it difficult to house the vacuum pad structure in the same conveying layout as in the conventional page turning apparatus using buckling distortion.